The Islamic State released photos showing the destruction of six priceless artifacts from the ancient city of Palmyra. The photos show jihadis taking a sledgehammer and smashing the historic treasures, including one dating from the second century.

Jihadis took sledgehammers to the relics, smashed them to pieces and then lashed the man who allegedly smuggled the artifacts in a public square full of onlookers, the Islamic State announced Thursday [Screenshots from Islamic State propaganda video]

Jihadis took sledgehammers to the relics, smashed them to pieces and then lashed the man who allegedly smuggled the artifacts in a public square full of onlookers, they announced on social media Thursday.

One-fifth of Iraq's approximately 10,000 world-renowned cultural heritage sites are under the Islamic State's control and most have been heavily looted, Irina Bokova, the head of the U.N. cultural agency UNESCO, warned experts in London Thursday. Some Syrian sites have been so badly ransacked that experts say they no longer have historical or archaeological value.

The statues were discovered and deemed icons under ISIS's radical interpretation of Shariah law [Screenshots from Islamic State propaganda video]

"Violent extremists don't destroy [heritage] as a collateral damage, they target systematically monuments and sites to strike societies at their core," Bokova said Wednesday.

The 2,000-year-old Allat God statue, which depicts a lion catching a deer between its feet, is believed to have been destroyed Saturday. "ISIS terrorists have destroyed one of the most important unearthed statues in Syria in terms of quality and weight...it was discovered in 1977 and dates back to the second century A.D.," Ma'moun Abdul-Karim, director of museums and antiquities, told Syrian state-run news agency SANA Thursday.

The Lion of Al Lat statue at the Temple of Allat in Palmyra [Credit: Alamy]

It's "the most serious crime they have committed against Palmyra's heritage," he added to the AFP.

The militants have also planted improvised explosive devices (IEDs) around the ruins of the ancient city. The explosives appear placed according to a pattern that indicates they are set to optimize the "filmed destruction," says Michael Danti, co-director of the Syrian Heritage Initiative at the American Schools of Oriental Research, a group monitoring cultural damage in Syria and Iraq.

"The deliberate destruction, what we are seeing today in Iraq and Syria, has reached unprecedented levels in contemporary history," said Bokova.